I'm not a big fan of the Toro branded Loncin engines. At work I have replaced dozens of Kohler and Briggs head gaskets, many without signs of restricted airflow. 0 Kawasaki.
I have about 475 hours on my liquid cooled V-Twin Kawasaki, it's a 2009 vintage. I had to replace 1 coil pack last year. While I had it down I did the valve adjustment, changed coolant. Normal maint. every year.
I have 285 hrs on our Briggs 20 HP single with zero problems. I service it at the end of the season and its on our 42 inch cut Husqvarna that me bought from a dealer in OPE. Salesman told us not to get the Koehler because 20 years ago they were having problems. Ours has the hydrostat with a cooling fan on top and we have had no problems with it.